Artillery shells typically utilize a fuse installed at the leading end of the shell. The fuse is a mechanical or electronic device designed to control the detonation of the explosive charge of the shell. Modern artillery fuses further include electronics and telemetry systems for improved accuracy and detonation control. The electronic circuits disposed in the fuse remain in radio-frequency contact with a ground station after launch of the shell for coordinating the trajectory of the shell, making course corrections as necessary. Further, the artillery fuse may operate in conjunction with a satellite based positioning system, such as the NAVSTAR global positioning systems (GPS), maintained and operated by the United States government, for accurately determining the coordinates of the shell as it travels along its trajectory and reaches the point of impact, and for correcting the trajectories of subsequently fired munitions. GPS may also be used, as a positional reference, to deploy the flaps, from a previous free fall state, to more accurately control the downward descent to the target.
An artillery fuse having telemetry and positioning system electronics requires an antenna suitable for the application and environment to which an artillery shell is subject. The fuse antenna should be able to survive the extreme acceleration and high rotational velocities typical of gun launched projectiles. Further, the radiation pattern of the antenna should exhibit relatively high gain in the aft direction, the direction opposite to the direction of travel of the shell. The radiation pattern of the antenna should be minimal in the direction of travel of the shell to minimize or prevent jamming from the vicinity of the target area of the shell. Such an antenna should be of a sufficiently reduced size so as not to occupy a large of space within the interior of the fuse, and is desirably designed for operation with L-band and S-band signals. ("L" is the letter designation for microwave signals in the frequency range from 1 to 2 GHz, and "S" is the letter designation for microwave signals in the frequency range from 2-4 GHz.)
One prior art approach is described in the above-referenced patent application. While this design has considerable benefits, it does have some drawbacks. First of all, the size and shape of the antenna prohibit its use with some artillery shells having centrally disposed actuation pins for controlling airfoil surfaces on the artillery shell. The radiation pattern of the antenna is omni-directional in orthogonal directions about the shell trajectory and, therefore, is capable of being jammed from terrestrial positions.
Consequently, there exists a need for improved methods and systems for guiding artillery shells.